Adv. Mater. http://doi.org/f97kmx (2017)

The efficiency of solar-driven water evaporation devices, useful for applications such as desalination, can be enhanced using micro- or nanofabricated structures to improve broadband light absorption, optimize thermal management and create more water pathways. However, the added cost and complexity of utilizing such structures is not always acceptable. Now, Ning Xu and colleagues at Nanjing University have found that a readily available natural structure, the shiitake mushroom, can enable 78% conversion efficiency under 1 sun illumination. The mushroom's dark 'umbrella' aids light absorption while the porous portion underneath the umbrella as well as the fibrous stipe (stalk) help transport water. In their experiments, a supermarket-purchased shiitake was floated in a beaker of water housed in a solar simulator. Mass change was measured during illumination and the evaporation rate determined. The team found that the light absorption can be increased by carbonizing the mushroom; total absorption went from 79% to 96% and conversion efficiency increased from 62% to 78%. The mushrooms were carbonized by heating them for 12 hours at 500 °C in Ar gas. The pore and microfibre diameters approximately halved during carbonization, improving capillary action.